A185239 Numbers n such that (11^n + 10^n)/21 is prime.

53, 421, 647, 1601, 35527

Offset

1,1

Comments

All terms are prime.

a(6) > 10^5.

Links

Table of n, a(n) for n=1..5.

Mathematica

Select[ Prime[ Range[1, 100000] ], PrimeQ[ (11^# + 10^#)/21 ]& ]

Prog

(PARI) is(n)=ispseudoprime((11^n+10^n)/21) \\ Charles R Greathouse IV, May 22 2017

Crossrefs

Cf. A057178, A128341, A181141, A187819, A217095, A213216.

Sequence in context: A244771 A074836 A142851 * A053736 A181968 A261537

Adjacent sequences: A185236 A185237 A185238 * A185240 A185241 A185242

Keyword

nonn,more

Author

Robert Price, Apr 05 2013

Status

approved